If you'd like to keep your operating systems and disks completely separate without having to keep cracking open your case, creating your own hard drive switch might work for you.

Computer building and modification site Extreme Tech has a tutorial on making a basic selector switch for the power cables of your SATA drives. Why would you want to do this? By selectively offering power to only one of the drives you have hooked up, you recreate the effect of completely swapping out the hard drive. Instead of multiple partitions and boot loader applications, the computer just boots to whichever drive is powered as though it were the only drive with an operating system in the computer. If you want to or need to maintain completely independent disks, the simple switch makes it hassle free. Other than sacrificing a couple power cables to the knife and doing a little basic soldering, there isn't anything fancy involved in the project.

Intrigued by the idea but not so hot with a soldering iron? The author of the tutorial sells a three-drive switch for $32. Alternately, and in a similar price range, you could pick up a single bay tray-less SATA rack that would let you pop hard drives in and out like cassettes—but you would lose the safety factor of keeping them all mounted safely in the case at all times. If you have your own solution for keeping operating systems and disks separate, tell us how in the comments below.